Organosilicon (OS) nitrile solvents have low flammability, broad electrochemical windows and excellent thermal stability, which make them promising materials for lithium ion battery (LIB) electrolytes. However, little is known about ion transport and salt dissociation of the lithium salts in organosilicon nitrile electrolytes. In this presentation, we report on the temperature dependence of the self-diffusion coefficients of lithium, fluorine and proton for 6 pure OS nitrile solvent/LiPF6 salt electrolytes from 295.0 K to 330.0 K measured by Pulsed Gradient Stimulated Echo (PGSTE) NMR experiments. Electrolytes were prepared from 3 OS nitrile solvents with varying levels of fluorination and having a concentration of LiPF6 salt at Li+-solvent molar ratios of 1:5 or 1:20. We found that 1H, 7Li and 19F diffusion coefficients increase with increasing temperature for all samples as expected, and mono-fluorinated solvent electrolytes have the highest 7Li and 19F diffusion coefficients. In addition, all dilute samples have higher 7Li and 19F diffusion coefficients than their concentrated counterparts. A general trend that the degree of LiPF6 salt dissociation decreases with increasing temperature is also observed. All dilute fluorinated samples have higher salt dissociation than the concentrated ones, but the dilute non-fluorinated electrolyte has the lowest salt dissociation observed among all samples. The lithium transference numbers for all organosilicon samples were in between 0.35 to 0.50, and the mono-fluorinated samples have the highest Li+ transference numbers, above 0.40 for all temperature ranges. Our studies on the solvent, Li+ cation and PF6- anion diffusion help to illustrate the ion transport processes of lithium salts in the organosilicon nitrile solvent-based electrolytes. These electrolytes were synthesized by Silatronix® Inc.

NMR measurements of ion and solvent transport for organosilicon nitrile electrolytes

255th National Meeting (2018)

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